92 ANNUAL REPORT SMITHSONIAN INSTITUTION, 193 4 



first, or those with the highest turn of speed, or what? What little 

 extra have thty that the others haven't got? 



It seems to be nothing more than pure good luck. We know of 

 no way of increasing the chances of individual electrons; each just 

 takes its turn with the rest. It is a concept with which science has 

 been familiar ever since Rutherford and Soddy gave us the law of 

 spontaneous disintegration of radioactive substances — of a million 

 atoms 10 broke up every year, and no help we could give to a 

 selected 10 would cause fate to select them rather than the 10 of 

 her own choosing. It was the same with Bohr's model of the atom ; 

 Einstein found that without the caprices of fate it was impossible 

 to explain the ordinary spectrum of a hot body; call on fate, and 

 we at once obtained Planck's formula, which agrees exactly with 

 observation. 



From the dawn of human history, man has been wont to attribute 

 the results of his own incompetence to the interference of a malign 

 fate. The particle-picture seems to make fate even more powerful 

 and more all-pervading than ever before ; she not only has her finger 

 in human affairs, but also in every atom in the universe. The new 

 physics has got rid of mechanistic determinism, but only at the price 

 of getting rid of the uniformity of nature as well ! 



I do not suppose that any serious scientist feels that such a state- 

 ment must be accepted as final; certainly I do not. I think the 

 analogy of the beam of light falling on the dirty windowpane will 

 show us the fallacy of it. 



Heisenberg's mathematical equation shows that the energy of a 

 beam of light must always be an integral number of quanta. We 

 have observational evidence of this in the photoelectric effect, in 

 which atoms always suffer damage by whole quanta. 



Now this is often stated in parable form. The parable tells us 

 that light consists of discrete light-particles, called photons, each 

 carrying a single quantum of energy. A beam of light becomes a 

 shower of photons moving through space like the bullets from a 

 machinegun; it is easy to see why they necessarily do damage by 

 whole quanta. 



When a shower of photons falls on a dirty windowpane, some of 

 the photons are captured by the dirt, while the rest escape capture 

 and get through. And again the question arises: How are the 

 lucky photons singled out? The obvious superficial answer is a 

 wave of the hand toward Fortune's wheel; it is the same answer 

 that Newton gave when he spoke of his "corpuscles of light " experi- 

 encing alternating fits of transmission and reflection. But we read- 

 ily see that such an answer is superficial. 



